Such gas generators are designed for automobile safety.
One of the applications of such a generator is for inflatable safety restraint systems, called airbags.
These generators serve to ignite the two pyrotechnic charges located in two different chambers from a single igniter located in one of the chambers.
Various devices of this type are known in the state of the art.
Thus, document FR-A-2 877 428 describes a generator comprising a tubular casing subdivided inside by two partitions that define three contiguous chambers, i.e., two combustion chambers each containing a pyrotechnic charge on either side of a pacification chamber communicating with a discharge opening provided in the casing. These partitions have an opening forming a duct that allows a controlled passage of the hot gas generated by combustion of the pyrotechnic charge from the combustion chambers to the pacification chamber, this gas then escapes the pacification chamber via the discharge opening to inflate an airbag. A single first combustion chamber is provided with a charge igniter, so that a part of the gas generated by the combustion of the charge of the first chamber passes through the pacification chamber and enters the second combustion chamber that does not have an igniter, where it induces the combustion of the charge present there, to go out through the discharge opening via the pacification chamber.
Document EP-B-836 563 describes a tubular generator with two chambers each containing propellant and separated from one another by a barrier preventing passage of the flame front generated by the initiator located in one of the chambers to directly induce the combustion of the propellant located in the other chamber. Instead of this, the heat generated by the combustion of the propellant of one chamber induces the delayed ignition of the propellant by convection and/or conduction forced through openings and a compartment surrounding both chambers.
Document U.S. Pat. No. 7,204,512 B2 describes a generator having a first chamber containing a first gas generator composition and a second chamber containing a second gas generator composition and a sympathetic initiation device for sympathetic ignition of the second composition in response to the combustion of the first composition. This sympathetic ignition device is in a partition separating the two chambers and includes a head and a shaft to communicate heat from the first chamber to the second chamber to ignite a self-initiation material located at the end of the shaft in the second chamber. This self-initiation material, with an ignition temperature less than that of the second composition, thus ignites this composition.
Document U.S. Pat. No. 7,073,820 B2 describes a generator in which igniting an initiator located in a first chamber induces the combustion of a first pyrotechnic charge located in this chamber, which generates combustion products that propagate through an opening initially closed by a cap to ignite a second gas generator composition located in a second cavity; the gas then escapes to the outside by openings made in this second cavity.
Document EP-A-733 519 describes a gas generator having two separate chambers, which each contain a gas generator material and an initiator for igniting the material to generate the gas and rapidly fill an airbag. The two chambers are separated by a wall provided with a cap, which is broken in response to a predetermined pressure level of the first of the chambers to allow the communication of fluids between the two chambers and which is supported by a support ring with a small-diameter central opening, so that, when the pyrotechnic gas generator material of the second chamber is ignited by the initiator found therein, the cap resists the increase in pressure of the second chamber, so that the gas pressure of the second chamber is confined therein and is not communicated to the first chamber.
Document U.S. Pat. No. 4,950,458 describes a gas generator according to the preamble of claim 1.
Today, many gas generators use pyrotechnic charges made up of pellets of propellant instead of blocks, for reasons of feasibility, the propellant manufacturing process, the density of the charge or the manufacturing cost of the propellant.
However, a first major disadvantage of pellets is that they have a shape function which is degressive, thus generating the maximum gas at the start of the operation, which can cause damage to the dashboard and its surroundings (breakage, deformation of the frame).
This disadvantage is especially important for pyrotechnic gas generators with a single igniter.
Moreover, a second requirement of current gas generators is that they must pass strict regulatory tests for safety, which require preventing fragmentation of the generator when the generator is subjected to an external heat source.
In order to verify this, the generators can be positioned on top of burners until their pyrotechnic charge(s) combust(s) by self-initiation of the pyrotechnic charge.
This characteristic is verified, for example, by a test required for regulations pertaining to transport of hazardous materials: the ONU6C test. Generators are positioned over a fire until they are triggered (by self-ignition of the pyrotechnic charge). The generators must be undamaged after triggering. The later the triggering occurs after the generator is heated or the fire is started, the more fragile the generator structure and the greater the risk of fragmentation.
A third requirement is also to improve the reproducibility of generator operation.